1. Field of the Invention
The present invention relates to improvements in hydraulic pumps.
2. Brief Description of the Prior Art
Hydraulic pumps and actuating cylinders provide an effective means for positioning an object with respect to its surroundings and are, accordingly, in widespread use. For example, as disclosed in U.S. Pat. No. 4,482,330 issued Nov. 13, 1984 to Cook, there are advantages to adjusting the height of an outboard motor on the transom of a boat during operation of the boat and such positioning can be efficiently carried out by mounting the motor on a motor bracket that is slidably mounted on a transom bracket that is, in turn, mounted on the transom of the boat. Vertical movement of the motor can then be effected by a hydraulic actuating cylinder that is connected between the two brackets and operated by pressurized hydraulic fluid supplied by a hydraulic pump.
U.S. Pat. No. 4,482,330 provides an illustration of demands that are often made on hydraulic pumps. In order for the pump used in the motor mounting apparatus described in U.S. Pat. No. 4,482,330 to carry out the purpose intended, it must meet a number of requirements. Not only must the pump be reversible (that is, capable of delivering hydraulic fluid under pressure from either of two ports while receiving return fluid into the other port), it must also provide a positive seal against fluid flow once the motor has been placed at a desired position. Moreover, these requirements must be reliably met by a pump of reasonable size that can be mounted on the transom bracket. Of equal importance, these characteristics must be met by a pump that can be obtained at a reasonable cost from a dependable source of supply. Since the outboard motor mounting apparatus is a consumer item, excessively expensive components will limit the market for the apparatus; similarly, if the source is not dependable, difficulties will arise in meeting the demand to again affect the market for the product.
In the past, the totality of these requirements has created a problem for the manufacturer of a product in which a hydraulic pump would be well suited for carrying out the operation of the product. The manufacturer may not be able to obtain a suitable pump at a price that will make its product competitive, or low cost pumps that are available may not be well suited for its product. Moreover, the manufacturer may very well not be in a position to manufacture the pumps itself to meet its requirements. If the product is a specialty item, the cost of tooling up to manufacture the pump (primarily the cost of casting pump bodies to include various chambers and flow passages) may not be recoverable from sales of the product. The net result is that the manufacturer may have to use a pump that is not optimally suited for its product but that is available at a reasonable price. Moreover, should the source of pumps dry up, for example, by a discontinuance of manufacture of the pump, the manufacturer must find a new source of supply, requiring a compromise between pump characteristics and pump costs. In the worst case, the manufacturer may not be able to find a suitable pump at a suitable price.